A conventional navigation device, such as a car navigation system, has a function of searching a route from a place of departure to a destination. Generally, such a navigation device also has a function of rerouting (researching a route afterwards) when a current location that is determined by a Global Positioning System (GPS) is deviated by more than a predetermined distance from a route that was searched and selected at the place of departure. The rerouting is performed automatically, since an operation of the navigation device by a user while driving the vehicle is dangerous.
Some navigation devices perform the automatic rerouting under a predetermined condition. For example, the following patent document 1 discloses a technology that does not perform the rerouting when a vehicle is near any point on the route to the destination, even if the vehicle has deviated from the route.
Moreover, the following patent document 2 discloses a technology that displays, according to a request from a user, a new route that was researched and stored in the navigation device in the background (irrespective of whether the automatic rerouting setting has been done or not) when the vehicle was deviated from a route to the destination.
On the other hand, in recent years, a navigation device not only for a car driver but also for a user who is walking or taking a train or a bus has been proposed (refer to the following patent document 3, for example).    Patent document 1: Japanese Patent Application Laid-open Publication No. H8-159797    Patent document 2: Japanese Patent Application Laid-open Publication No. H9-152352    Patent document 3: Japanese Patent Application Laid-open Publication No. 2000-258184